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Comm Port CTS handshaking - need help

Discussion in 'Hardware' started by unixguy, Oct 10, 2003.

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  1. unixguy

    unixguy Thread Starter

    May 24, 2003
    I am trying to connect the comm port of a PC to a FANUC CNC controller to upload CNC programs (pure ASCII text). The FANUC uses CTS handshaking for flow control (I think). The COMM port on the PC only has 2 options for handshaking, "Software" and "Hardware". I have tried both and neither seems to provide any handshaking (I have BUFFER OVERFLOW on the FANUC every time I send). The other parameters (Baud, Parity, Word Length, Stop Bits) seem ok because the data that arrives is readable, it just is partly overwritten.
    Regarding the COMM port, I assume that "software" is XON-XOFF but I do not know if "Hardware" is CTS or DTR-type handshaking. From what I can tell, almost everyone refers to CTS as "hardware" handshaking but from the description of it, it sounds like it is really more like software handshaking. That is, the computer sends out an RTS signal, the device responds with a CTS signal ("software"?) in order for transmit to start, as opposed to DTR which is simply a voltage ("hardware") that goes high or low to control the flow.
    Anyway, does anyone know which type of handshaking is really meant by "hardware" on a PC comm port? I need to know which line to monitor in order to see if any handshaking signal is really happening at all. Also, does anyone know of any diagnostic software that runs on the PC to notify me if it sees any handshaking signal at all?
    Thanks for any help you can give.
  2. Lurker1


    Jan 30, 2001
    Its been too long since I have done anything link this but hardware hangshaking uses hardware controlled lines to communicate between the PC and software uses special characters to communicate. With the right software you can set the start character and stop character and start bits etc. You would first need to know what the terminal you are sending to expects and match the sending terminal to it. I guess you are using a program like Hyperterminal to do this with? In the old days of communications you used a breakout box to match the signals you needed and some of these had Leds on them to monitor the state of the communication signals.

    Some references (but I'm sure there are better ones someplace.)



    Depending on the wiring of the CNC machine you may need to be using a null modem cable to connect the two. My knowledge of connecting pcs to CNCs is pretty limited . Good Luck.
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